Superheat control for refrigerating apparatus



p 1948. I c. E. WINCHESTER ETAL 2,449,437

SUPERBEAT CONTROL FOR REFRIGERA'I'ING APPARATUS r;1a lay 21. 1947 Inventofs Clark E.Winchesber, Harold FZLathr op, y QM I Their Attorney.

Patented Sept. 14, 1948 SUPERHEAT CONTROL FOR REFBIGERAT- v ING APPARATUS Clark E. Winchester, Roanoke, Ind., and Harold F. Lathrop, Philadelphia, PI, a'ssignors to General Electric Company, a corporation of New York Application May 21, 1947, Serial No. 150,112.

' 6 Claims.

1 This invention relates to refrigerating apparat'us'and particularly to a flow regulating device for controlling the supply of liquid refrigerant to such apparatus in accordance with the superheat of the vaporized refrigerant withdrawn from the evaporator. In certain applications of refrigerating machines of thejcompression type, it is necessary to provide a highdegree of sensitivity in the refrigerant flow controlling device which admits liquid refrigerant to the evaporator. It is a common practice to employ thermostatic expansion valves for this purpose. These valves include a control element responsive to the pressure of the refrigerant in the evaporator and a second control element responsive to thetemperature of the vaporized refrigerant withdrawn from the evaporator. These two elements are connected in bucking relation and effect control of the refrigerant to maintain a substantially constant amount of superheat in the vaporized refrigerant. In systems requiring high control sensitivity; for example in systems operating at very low temperature, such as those employed in testing internal combustion engines for high altitude operation, the conventional thermostatic expansion valve may be found unsatisfactory. Accordingly, it is an object of this invention to provide a superheat control for refrigerating'machines which aiiords a high degree of sensitivity to changes in pressure and temperature within the evaporator.

It is another object of this invention to provide improved thermostatic expansion valves for refrigerating. machines including a device for boosting the actuating force of the valve to secure increased'sensitivity over a wide range of operating conditions.

Further objects and advantages of the invention will become apparent as the following description proceeds, and the features of novelty which characterize the invention will be pointed out with particularity iii the claims annexed to and forming a part of this specification.

For a better understanding of this invention, reference maybe had to the accompanying drawing in which Fig. 1 represents diagrammatically a refrigerating system embodying the invention;

Fig. 2 is a schematic circuit diagram of an electronic amplifier for one embodiment of the in- .vention; and Fig. 3 is a circuit diagram of an evaporator pressure and suction gasjtemperature controls. In addition to the normal control, thevalve is provided with a booster control actuated in accordance with the temperatures of the inlet and outlet of the evaporator as determined by a pair of thermocouples which produce a voltage proportional to the amount of superheat in the vaporized refrigerant. The voltage produced by the thermocouples is amplified electronically and issupplied to a solenoid for boosting the action of the thermostatic expansion valve. In one embodiment, a modulating action is secured, the boosting force being proportional throughout the range of operation to the amount of superheat in the vaporized refrigerant, and in a second embodiment an "on-oil. operation is employed, the

thermostatic expansion valve being closed whenever, the superheat exceeds a predetermined value.

Referring now to the drawing, the refrigerating system illustrated in Fig. 1 comprises a coin-- erant enters a receiver 3 from which .it is supplied to two evaporators t and 5 under control of thermostatic expansion valves 6 and 1 respectively.

The liquid refrigerant is vaporized by the absorption of heat and the vaporized refrigerant is returned to the compressor I from the-evaporators 4 and 5 through suction lines Band 9 respectively. The evaporator 4 is arranged to cool a compartment indicated by a dotted line I0, and the evaporator 5 a compartment II. The valves i5 and I are provided with solenoids i2 and I 3 respectively connected through'thermostats I4 and ii to a suitable current supply It. Eachof the thermostats II and i5 is set to energize its solenoid when the temperature in the'corresponding compartment is below a predetermined minimum value;

The valve 6 is provided with an expansible diaphragm I'l connected by a rod I8 to avalve member IL Liquid flows from the receiver 3 through a liquid line 20 and, when the valvel! is in its open position, is admitted to the evaporator through a second portion of the liquid line. A" lower side of'the diaphragm I1 is thus subjected to the pressure. in the evaporator. The

upper side of the diaphragm i1 is enclosed in a pressure-tight chamber 22 connected to a temperature feeler bulb 23 by the usual pressure transmitting tube 24. The diaphragm I! thus moves to open the valve is on an increase in pressure in the chamber 22 and on a decrease in evaporator pressure below the diaphragm, an increase in evaporator pressure tending to close the valve.

1 The operation in accordance with the resultant difference in pressure controls the' flow of refrigerant to the evaporator so that the superheat in the vaporized refrigerant withdrawn from the driving the valve is relatively small because the change in pressure is relatively small for a change in temperature as compared with the operation of the valve at higher temperatures. For this reason, accurate control of superheat becomes difficult. In order to overcome the inherent sluggish operation of the valve 6 at low temperatures, a second solenoid indicated at 26 is arranged below the solenoid i2 and in a position to produce a magnetic field for moving the plunger 25. The second solenoid is actuated in accordance with the superheat of the refrigerant as determined by a pair of thermocouples 2'! and 28 secured adjacent theinlet and outlet of the evaporator and connected in a series circuit tofan electronic amplifying device 29 which energizes'the solenoid through leads 30. The thermocouples 21 and 28 are connected in bucking relation so that the combined voltage generated is proportional to the difference in temperatures at the two points and consequently is proportional to the superheat of the vaporized refrigerant. The response of the thermocouple circuit to changes in temperature is substantially instantaneous, and by utilizing the amplifying device 29 it is possible to exert a substantial force on the valve I9 in the .same direction as the force of the normal superheat control but with a speed of response substantially greater than that of the normal control. As a result, when the system is operating at low tem-* peratures the superheat is controlled effectively even though the conventional control would otherwise be sluggish. The thermostatic expansion valve 1 is provided with a similar control including thermocouples 3i and 32 at the inlet and outlet respectively and an amplifier 33 connected to a solenoid 34 by leads 35., Because of the high speed of response, the superheat of the refrigerant va or withdrawn from both the evaporators 4 and 5 may be accurately controlled over a wide range of pressures and temperatures. For example, the system may be operated with satisfactory. control of superheat throughout the cordance with the superheat of the suction gas period of pull-down when the compressor is started with the system at room temperature. The electronic amplifiers 29 and 33 are so connected that their outputs provide energization of the solenoids 26 and 34 in proportion to the voltage differences measured by the respective pairs of thermocouples. The amplifiers thus provide continuous energization of the solenoids in acand modulated operation of the valves 6 and 1 installations the amplifiers 29 .and 33 may be arranged to energize the solenoids and to retain the valve in its open position regardless of the condition of operation of the other actuating elements whenever the temperature difference be tween the inlet and'outlet thermocouples exceeds a predetermined value. Types of these two forms of amplifiers are illustrated by way of example in Figs. 2 and 3.

Referring now to Fig. 2, the amplifier 29 as illustrated therein comprises a transformer 36 having its primary winding connected in series with the thermocouples 21 and 26 and with a variable resistance device 31. The variable resistance device as illustrated comprises a pair of carbon blocks 38 arranged in contact. The pressure between the blocks 38 is varied continuously by pressure exerted by a solenoid 39 excited by alternating current. say at 60 cycles. The resistance of the device 31 is thus varied continuously in accordance with the alternating current wave and any current produced by the thermocouples ,2! and 28 is thus varied and may be impressed on an electron discharge device 40 by connecting the secondary of the transformer between a control electrode 4| and a cathode 42 in series with a resistor 43. The device 40 includes an anode 44 connected in an output circuit including the primary winding of a transformer 45 and a suitable source of direct current, such as a battery 46.

' The secondary of the transformer 45 is connected to supply a pair of electron discharge devices 41 and 48 connected in push-pull relationship and having their outputs connected to the primary of the transformer 49, the secondary winding of which is connected in a circuit including two electron discharge devices 50 and 5| for rectifying the output of the transformer 49 and for supplying -rectified current across a capacitor 52 to the solenoid 26 through the leads 30. This amplifier is effective to utiliie the very weak output voltage of the pair of thermocouples 21 and 28 to supply a current proportional to the voltage and suflicient for actuating the solenoid 26 and supply a booster action for assuring a quick response of the actuatin elements of the thermostatic expansion valve in accordance with changes of conditions in the evaporator.

The "on-off typeof electronic amplifier is illustrated in Fig. 3 and is connected in the same position as the amplifier 29, corresponding parts of the system being indicated by the same nu-' merals. As shown in Fig. 3, the pair of thermocouples 21 and 26 are connected in a series circuit including a resistance 53 and a galvanomete or millivoltmeter coil 54. Energization of the coil 54 varies the position of a vane 55 and, on a predetermined maximumdifference in' voltage representing a maximum difference in temperature between the thermocouples, the .vane 55 moves into the magnetic field between coils and 68 resulting'in the stopping of oscillation and suilicient increase in anode current-to close a relay of the device 51 and the cathode 62, the coil of the relay 58 being included in the anode circuit. The electron discharge device. 51 also includes a screen grid the potential of which may be adjusted by adjusting a potentiometer 68 connected across a portion of the secondary winding of a transformer 61.

the relay 58 and is continuously energized by alternating current from, the line 59 which is connected to the primary of the transformer. A feedback circuit for effecting oscillation comprises a coil 68 connected between the cathode 62 which is at ground potential, and the anode 84 through a capacitor 69. The vane 55 is arranged to move between the coils 60 and 88 and change the coupling therebetween, the oscillator beingnot by way of limitation.

While this invention has been illustrated in connection with a refrigerating machine having a plurality of evaporators, other applications will readily be apparent to those skilled in the art.

It is not, therefore, desired that the invention be limited to the particular constructions illusrated and described, and it is intended by the appended claims to cover all modifications within the spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United Statesis:

1. In a refrigerating apparatus including an evaporator and means for supplying liquid refrigerant thereto and for withdrawing vaporized refrigerant therefrom, a thermostatic expansion valve including actuating means dependent upon The transformer 81 is connected in the load circuit between the cathode 82 and the superheat of the vaporized refrigerant for controlling the admission of liquid refrigerant to said evaporator, means responsive to the temperatures at the inlet and outlet of said evaporator for producing an electric voltage proportional to the difference between the inlet and outlet temperatures; and means dependent upon said voltage for applying a boosting force to said actuating means.

2. In a refrigerating apparatus including an evaporator and means for supplying liquid refrigerant thereto and'for withdrawing vaporized refrigerant therefrom, a thermostatic expansion' tween the inlet and outlet temperatures. and

means dependent upon said voltage for applying a boosting force to said valve in the same-direction as the resultant force on said elements.

3. In a refrigerating apparatus including an evaporator and means for supplying liquid refrigerant thereto and for withdrawing vaporized refrigerant therefrom, a thermostatic expansion valve, including actuating means dependent upon the superheat of the vaporized refrigerant for controlling the'admission of liquid refrigerant to said evaporator, means responsive to the temperatures at the inlet and outlet of said evaporator for producing an electric voltage proportional to the difference between the inlet.

and outlet temperatures, and means dependent upon a predetermined maximum value of said voltage for retaining said valve in its open position regardless of the condition of said actuating means.

4. In a refrigerating apparatus including an evaporator and means for supplying liquid refrigerant thereto and for withdrawing vaporized refrigerant therefrom, a thermostatic expansion valve including actuating means dependent upon the superheat of the vaporized refrigerant for controlling the admission of liquid refrigerant to said evaporator, means including thermocouples secured to said evaporator near the inlet and outlet thereof and connected in opposing relation in a series circuit for producing, a voltage proportional to the difference between the inlet and outlet temperatures, and means dependent upon said voltage for applying to said actuating means a boosting force proportional to the difference between the inlet and outlet temperatures of said evaporator.'

5. In a refrigerating apparatus including an evaporator and means for supplying liquid reposing relation in a series circuit for'producing' a voltage proportional to the difference between the inlet and outlet temperatures, and means in cluding an electronic amplifier responsive to said voltage for applying to said actuating means a boosting force proportional to the difference between the inlet and outlet temperatures of said evaporator.

6. In a refrigerating apparatus including an evaporator and means for supplying liquid refrigerant thereto and for withdrawing vaporized refrigerant therefrom, a thermostatic expansion valve for controlling the admission of liquid refrigerant to said evaporator in accordance with the superheat of the vaporized refrigerant withdrawn therefrom, said valve including opposed actuating elements responsive respectively to the pressure within said evaporator and the temperature of the refrigerant withdrawn therefrom, a pair of thermocouples one connected near the inlet and the other near the outlet of said evaporator for producing an electric voltage proportional to the diflerence between the inlet and outlet temperatures, and means including an electronic amplifier responsive to said voltage for applying to said valve a boosting force proportional to said diiference in temperature throughout the normal range of operation of said valve.

CLARK E. WINCHESTER. HAROLD I". LATHROP. 

